An optical transmission spectrum of the giant planet WASP-36 b

TL;DR

This study provides a detailed optical transmission spectrum of the giant exoplanet WASP-36 b, revealing a significant decrease in planetary radius from blue to red wavelengths, indicating atmospheric absorption features.

Contribution

It presents the first high-precision multi-band photometry of WASP-36 b's transits, deriving an optical transmission spectrum and identifying strong blue-wavelength absorption.

Findings

Detected a radius decrease of ~11 pressure scale heights from g to z bands.

Observed a >5 sigma confidence level for the radius variation.

Indicated presence of atmospheric species absorbing at blue wavelengths.

Abstract

We present broad-band photometry of five transits in the planetary system WASP-36, totaling 17 high-precision light curves. Four of the transits were simultaneously observed in four passbands (g, r, i, z), using the telescope-defocussing technique, and achieving scatters of less than 1 mmag per observation. We used these data to improve the measured orbital and physical properties of the system, and obtain an optical transmission spectrum of the planet. We measured a decreasing radius from bluer to redder passbands with a confidence level of more than 5 sigma. The radius variation is roughly 11 pressure scale heights between the g and the z bands. This is too strong to be Rayleigh scattering in the planetary atmosphere, and implies the presence of a species which absorbs strongly at bluer wavelengths.